Starting a selfmade c++ application via Qprocess

christophator

Hi,
i have a QT widget app. wich starts a c++ application via QProcess.
I wrote this on win10 and now i have to install it on linux/debian9.

I changed the path in linux format. Compiled the c++ application on my debian system.
But it won't start.
Here is the code:

Constructor:

TemperaturMessung::TemperaturMessung(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::TemperaturMessung)
{
    ui->setupUi(this);
    process = new QProcess(this);
    process->setProcessChannelMode(QProcess::MergedChannels);
    program = "./Dokumente/Tempmess/Sources/Comreader/Tempmess";  //Tempmess is the c++ aplication wich i want to start
    fileName = "/Dokumente/Tempmess/Messprotokolle";
    ui->speicherOrt->insert(fileName);
    connect( process, SIGNAL(readyReadStandardOutput()), this, SLOT(processOutput()) );
    connect( process, SIGNAL(readyReadStandardError()), this, SLOT(processOutput()) );
    connect( process, SIGNAL(started()), ui->startButton, SLOT(hide()));
    connect( process, SIGNAL(finished(int,QProcess::ExitStatus)), ui->startButton, SLOT(show()));

}

Function which starts the process:

void TemperaturMessung::on_startButton_clicked()
{
   //bla bla...

    QStringList argv;
    argv << abtastStr << kanalStr << dauerStr<<fileName;
    process->start(program,argv);
    process->waitForStarted();
}

Is there anything i have to do with my self compiled programm (The Tempmess thing)?

Thanks for help!

koahnig

@christophator

Hi and welcome to devnet forum

Looks like you got messed up with path issues.

    program = "./Dokumente/Tempmess/Sources/Comreader/Tempmess";  //Tempmess is the c++ aplication wich i want to start
    fileName = "/Dokumente/Tempmess/Messprotokolle";

The program path is a relative path starting at your current working.
The fileName path is an absolute path. It does not really look as a typical linux path.

You can check the currentPath

qDebug() << QDir::currentPath();

From there you can check if the rest ist ok.

Alternatively I would recommend starting with fixed complete absolute path' which typically helps to get an overview.
Also you need to check that your C++ application is starting outside in a terminal.

Pablo J. Rogina

@christophator once you solve the issue with the *nix path, you may want to consider using some configuration file (i.e. via QSettings class) to store the path/arguments of the external C++ app to launch so to avoid recompiling your Qt application for Linux, WIndows, etc everytime the path/platform changes

JonB

@christophator
You should discover why it "did not start" under Linux if you add signal/slot for http://doc.qt.io/qt-5/qprocess.html#errorOccurred. You have done well hooking up the other signals, but you really need that one too, especially for production.

christophator

@koahnig and @Pablo-J-Rogina thank you very much!

I didn't understand how the linux paths work.

I put my c++ application into the current folder of the Qt program and called only the name in the program path.
There it works :)
Now I will get into the QDir and QSettings class to solv it properly.

JonB

@christophator
Linux paths work more-or-less identically to Windows ones, just they use / instead of \ and don't have a crazy drive letter.

christophator

@JonB
Yeah :D and I didn't realized that I used a ralative path wich starts at the current folder..
Now I got it!

JonB

@christophator
Any path which does not start (very first character) with a / (Linux) or \ (Windows) is relative. And under Windows be careful with drive letters: D:\fred is absolute but D:fred is actually relative, to the current directory on drive D:, whatever that is.

koahnig

@JonB said in Starting a selfmade c++ application via Qprocess:

@christophator
Linux paths work more-or-less identically to Windows ones, just they use / instead of \ and don't have a crazy drive letter.

Not exactly. That seem to reflect the blinker view of linux guys.

Windows does tolerate '/' for a long time already. Me, as a Windows boy, I simply switched to the forward slash long ago.

When you are not using linux for daily work, you ask yourself a lot where you can find that stupid device again.

JonB

@koahnig
Since you have chosen to question what I wrote (as a simplified answer), I shall return the favour by saying "Not exactly" to you!

Not exactly. That seem to reflect the blinker view of linux guys.
Windows does tolerate '/' for a long time already. Me, as a Windows boy, I simply switched to the forward slash long ago.

Nope. That's too simplistic, which is why I didn't mention it! Try each of the following:

dir \c
dir /c

They don't produce the same, do they? So it's not fair to say that Windows users can use / instead of \, is it? That seem to reflect the blinker view of Windows guys. :) This is only one example.....

koahnig

@JonB said in Starting a selfmade c++ application via Qprocess:

@koahnig
Since you have chosen to question what I wrote (as a simplified answer), I shall return the favour by saying "Not exactly" to you!

Not exactly. That seem to reflect the blinker view of linux guys.
Windows does tolerate '/' for a long time already. Me, as a Windows boy, I simply switched to the forward slash long ago.

Nope. That's too simplistic, which is why I didn't mention it! Try each of the following:
dir \c
dir /c
They don't produce the same, do they? So it's not fair to say that Windows users can use / instead of \, is it? That seem to reflect the blinker view of Windows guys. :) This is only one example.....

:D
Not sure, if it is the blinker view of Windows guy or of someone concentrating on a specific topic, the path issue, without mentioning it explicitly. ;) Also, if I am not mistaken, is the backslash used mainly for separation in a long path.

BTW Have fun to use in Windows

dir \c

which will not work. Also there the recommendation to use better a forward slash will help. ;)

Anyway I am not interested in specific linux nor windows bashing. Especially the backslash within a path and its special meaning within string drives probably most of the developers nuts. Therefore I am gladly using the forward slash whenever possible.

JonB

@koahnig

BTW Have fun to use in Windows
dir \c
which will not work.

? Of course it "works". dir \c means "list the file/directory named c in the root folder of the current drive". (If there isn't one, of course it reports File not found, but it's still "working".) OTOH, dir /c means "list all the files in the current directory on the current drive, passing the /c switch to dir". Quite different. Which is why I would never use or recommend / instead of \ for paths in Windows, and I'm surprised you get away with it in practice..... Not Linux vs Windows "bashing" (it was you who used the word "blinker"!), just a heads-up as to it's not robust enough to risk IMHO.....